Kazakhstan is the ninth largest country in the world and the fourteenth largest producer of wheat; in 2021 alone, the country produced 14.3 million tons (t) of wheat on 12.1 million hectares (ha). Despite this impressive figure, wheat yield in the country falls below average at 1172.5 t/ha compared to 3474.4 t/ha globally.
Research into wheat diseases in Kazakhstan has primarily revolved around airborne fungal foliar diseases, such as stem rust, leaf rust and stripe rust, which can be devastating for farmers and their crops. However, the effects of fungi relating to wheat root and crown root were yet to be examined – these diseases affect yields, stands and grain quality due to infections that cause damping-off, blight, necrosis, and dry rotting.
Using plant samples taken during the 2019 growing season, scientists from the International Maize and Wheat Improvement Center (CIMMYT) conducted a quantitative survey to determine the distribution of this fungi. Using morphological and molecular tools on 1,221 samples from 65 sites across the central, eastern, and southeastern region, scientists found that Bipolarissorokiniana and Fusariumacuminatum were the most predominant fungal species isolated.
In total, 74 isolates from 16 species were tested, revealing that F. culmorum and F. pseudograminearum, B. sorokinaiana, Fusarium sp., R. solani, F. redolens, C. spicifera, C. inaequalis, and N. orvzae were virulent fungi.
Results show the diverse spectrum of pathogenic fungal species linked to wheat crown and root rot in Kazakhstan and is highly likely to be the first report from the country on the presence of F. seudograminearum, Fusarium sp., C. spicifera, and C. inaequalis.
With this new data, scientists can develop mitigations to prevent crop loss and improve wheat yield across Kazakhstan.
Cover photo: The scientists from Turkey researching root and crown rot in Kazakhstani wheat: Abdelfattah A. Dababat (CIMMYT), Mustafa Imren (Bolu Abant Izzet Baysal University), Göksel Özer (Bolu Abant Izzet Baysal University) and Rauan Zhapayev. (Photo: Abdelfattah A. Dababat/CIMMYT)
Mustafa Alisarli, Bolu Abant Izzet Baysal University rector, is awarded for hosting this symposium by the representative of the Turkish Ministry of Agriculture and Forestry, General Directorate of Agricultural Research and Policies (GDAR), Dr Suat Kaymak.
The International Maize and Wheat Improvement Center (CIMMYT) coordinated the VIII International Cereal Nematode Symposium between September 26-29, in collaboration with the Turkish Ministry of Agriculture and Forestry, the General Directorate of Agricultural Research and Policies and Bolu Abant Izzet Baysal University.
As many as 828 million people struggle with hunger due to food shortages worldwide, while 345 million are facing acute food insecurity – a crisis underpinning discussions at this symposium in Turkey focused on controlling nematodes and soil-borne pathogens causing reduced wheat yields in semi-arid regions.
A major staple, healthy wheat crops are vital for food security because the grain provides about a fifth of calories and proteins in the human diet worldwide.
Seeking resources to feed a rapidly increasing world population is a key part of tackling global hunger, said Mustafa Alisarli, the rector of Turkey’s Bolu Abant Izzet Baysal University in his address to the 150 delegates attending the VIII International Cereal Nematode Symposium in the country’s province of Bolu.
Suat Kaymak, Head of the Plant Protection Department, on behalf of the director general of the General Directorate of Agricultural Research and Policies (GDAR), delivered an opening speech, emphasizing the urgent need to support the CIMMYT Soil-borne Pathogens (SBP) research. He stated that the SBP plays a crucial role in reducing the negative impact of nematodes and pathogens on wheat yield and ultimately improves food security. Therefore, the GDAR is supporting the SBP program by building a central soil-borne pathogens headquarters and a genebank in Ankara.
Discussions during the five-day conference were focused on strategies to improve resilience to the Cereal Cyst Nematodes (Heterodera spp.) and Root Lesion Nematodes (Pratylenchus spp.), which cause root-health degradation, and reduce moisture uptake needed for proper development of wheat.
Richard Smiley, a professor emeritus at Oregon State University, summarized his research on nematode diseases. He has studied nematodes and pathogenic fungi that invade wheat and barley roots in the Pacific Northwest of the United States for 40 years. “The grain yield gap – actual versus potential yield – in semiarid rainfed agriculture cannot be significantly reduced until water and nutrient uptake constraints caused by nematodes and Fusarium crown rot are overcome,” he said.
Experts also assessed patterns of global distribution, exchanging ideas on ways to boost international collaboration on research to curtail economic losses related to nematode and pathogen infestations.
A special session on soil-borne plant pathogenic fungi drew attention to the broad spectrum of diseases causing root rot, stem rot, crown rot and vascular wilts of wheat.
Soil-borne fungal and nematode parasites co-exist in the same ecological niche in cereal-crop field ecosystems, simultaneously attacking root systems and plant crowns thereby reducing the uptake of nutrients, especially under conditions of soil moisture stress.
Limited genetic and chemical control options exist to curtail the damage and spread of these soil-borne problems which is a challenge exacerbated by both synergistic and antagonistic interactions between nematodes and fungi.
Nematodes, by direct alteration of plant cells and consequent biochemical changes, can predispose wheat to invasion by soil borne pathogens. Some root rotting fungi can increase damage due to nematode parasites.
Integrated managementFor a holistic approach to addressing the challenge, the entire biotic community in the soil must be considered, said Hans Braun, former director of the Global Wheat Program at CIMMYT.
Braun presented efficient cereal breeding as a method for better soil-borne pathogen management. His insights highlighted the complexity of root-health problems across the region, throughout Central Asia, West Asia and North Africa (CWANA).
Richard A. Sikora, Professor emeritus and former Chairman of the Institute of Plant Protection at the University of Bonn, stated that the broad spectrum of nematode and pathogen species causing root-health problems in CWANA requires site-specific approaches for effective crop health management. Sikora added that no single technology will solve the complex root-health problems affecting wheat in the semi-arid regions. To solve all nematode and pathogen problems, all components of integrated management will be needed to improve wheat yields in the climate stressed semi-arid regions of CWANA.
Building on this theme, Timothy Paulitz, research plant pathologist at the United States Department of Agriculture Agricultural Research Service (USDA-ARS), presented on the relationship between soil biodiversity and wheat health and attempts to identify the bacterial and fungal drivers of wheat yield loss. Paulitz, who has researched soil-borne pathogens of wheat for more than 20 years stated that, “We need to understand how the complex soil biotic ecosystem impacts pathogens, nutrient uptake and efficiency and tolerance to abiotic stresses.”
Julie Nicol, former soil-borne pathologist at CIMMYT, who now coordinates the Germplasm Exchange (CAIGE) project between CIMMYT and the International Center for Agricultural Research in the Dry Areas (ICARDA) at the University of Sydney’s Plant Breeding Institute, pointed out the power of collaboration and interdisciplinary expertise in both breeding and plant pathology. The CAIGE project clearly demonstrates how valuable sources of multiple soil-borne pathogen resistance in high-yielding adapted wheat backgrounds have been identified by the CIMMYT Turkey program, she said. Validated by Australian pathologists, related information is stored in a database and is available for use by Australian and international breeding communities.
Economic losses
Root-rotting fungi and cereal nematodes are particularly problematic in rainfed systems where post-anthesis drought stress is common. Other disruptive diseases in the same family include dryland crown and the foot rot complex, which are caused mainly by the pathogens Fusarium culmorum and F. pseudograminearum.
The root lesion nematode Pratylenchus thornei can cause yield losses in wheat from 38 to 85 percent in Australia and from 12 to 37 percent in Mexico. In southern Australia, grain losses caused by Pratylenchus neglectus ranged from 16 to 23 percent and from 56 to 74 percent in some areas.
The cereal cyst nematodes (Heterodera spp.) with serious economic consequences for wheat include Heterodera avenae, H. filipjevi and H. latipons. Yield losses due to H. avenae range from 15 to 20 percent in Pakistan, 40 to 92 percent in Saudi Arabia, and 23 to 50 percent in Australia.
In Turkey, Heterodera filipjevi has caused up to 50 percent crop losses in the Central Anatolia Plateau and Heterodera avenae has caused up to 24 percent crop losses in the Eastern Mediterranean.
The genus Fusarium which includes more than a hundred species, is a globally recognized plant pathogenic fungal complex that causes significant damage to wheat on a global scale.
In wheat, Fusarium spp. cause crown-, foot-, and root- rot as well as head blight. Yield losses from Fusarium crown-rot have been as high as 35 percent in the Pacific Northwest of America and 25 to 58 percent in Australia, adding up losses annually of $13 million and $400 million respectively, due to reduced grain yield and quality. The true extent of damage in CWANA needs to be determined.
Abdelfattah Dababat, CIMMYT’s Turkey representative and leader of the soil-borne pathogens research team said, “There are examples internationally, where plant pathologists, plant breeders and agronomists have worked collaboratively and successfully developed control strategies to limit the impact of soil borne pathogens on wheat.” He mentioned the example of the development and widespread deployment of cereal cyst nematode resistant cereals in Australia that has led to innovative approaches and long-term control of this devastating pathogen.
Dababat, who coordinated the symposium for CIMMYT, explained that, “Through this symposium, scientists had the opportunity to present their research results and to develop collaborations to facilitate the development of on-farm strategies for control of these intractable soil borne pathogens in their countries.”
Paulitz stated further that soil-borne diseases have world-wide impacts even in higher input wheat systems of the United States. “The germplasm provided by CIMMYT and other international collaborators is critical for breeding programs in the Pacific Northwest, as these diseases cannot be managed by chemical or cultural techniques,” he added.
Closing ceremony of the International Cereal Nematode Symposium. From left to right; Hans Braun, Brigitte Slaats, Richard Sikora, Grant Hollaway, Mesut Keser, Zahra Maafi, Richard Smiley, Mustafa Imren, Fatih Ozdemir, Amer Dababat. (Photo: CIMMYT)
Road ahead
Delegates gained a greater understanding of the scale of distribution of cereal cyst nematodes and soil borne pathogens in wheat production systems throughout West Asia, North Africa, parts of Central Asia, Northern India, and China.
After more than 20 years of study, researchers have recognized the benefits of planting wheat varieties that are more resistant. This means placing major emphasis on host resistance through validation and integration of resistant sources using traditional and molecular methods by incorporating them into wheat germplasm for global wheat production systems, particularly those dependent on rainfed or supplementary irrigation systems.
Sikora stated that more has to be done to improve Integrated Pest Management (IPM), taking into consideration all tools wherever resistant is not available. Crop rotations for example have shown some promise in helping to mitigate the spread and impact of these diseases.
“In order to develop new disease-resistant products featuring resilience to changing environmental stress factors and higher nutritional values, modern biotechnology interventions have also been explored,” Alisarli said.
Brigitte Slaats and Matthias Gaberthueel, who represent Swiss agrichemicals and seeds group Syngenta, introduced TYMIRIUM® technology, a new solution for nematode and crown rot management in cereals. “Syngenta is committed to developing novel seed-applied solutions to effectively control early soil borne diseases and pests,” Slaats said.
It was widely recognized at the event that providing training for scientists from the Global North and South is critical. Turkey, Austria, China, Morocco, and India have all hosted workshops, which were effective in identifying the global status of the problem of cereal nematodes and forming networks and partnerships to continue working on these challenges.
As wheat blast continues to infect crops in countries around the world, researchers are seeking ways to stop its spread. The disease — caused by the Magnaporthe oryzae pathotype Triticum — can dramatically reduce crop yields, and hinder food and economic security in the regions in which it has taken hold.
Researchers from the International Maize and Wheat Improvement Center (CIMMYT) and other international institutions looked into the potential for wheat blast to spread, and surveys existing tactics used to combat it. According to them, a combination of methods — including using and promoting resistant varieties, using fungicides, and deploying strategic agricultural practices — has the best chance to stem the disease.
The disease was originally identified in Brazil in 1985. Since then, it has spread to several other countries in South America, including Argentina, Bolivia and Paraguay. During the 1990s, wheat blast impacted as many as three million hectares in the region. It continues to pose a threat.
Through international grain trade, wheat blast was introduced to Bangladesh in 2016. The disease has impacted around 15,000 hectares of land in the country and reduced average yields by as much as 51% in infected fields.
Because the fungus’ spores can travel on the wind, it could spread to neighboring countries, such as China, India, Nepal and Pakistan — countries in which wheat provides food and jobs for billions of people. The disease can also spread to other locales via international trade, as was the case in Bangladesh.
“The disease, in the first three decades, was spreading slowly, but in the last four or five years its pace has picked up and made two intercontinental jumps,” said Pawan Singh, CIMMYT’s head of wheat pathology, and one of the authors of the recent paper.
In the last four decades, wheat blast has appeared in South America, Asia an Africa. (Video: Alfonso Cortés/CIMMYT)
The good fight
Infected seeds are the most likely vector when it comes to the disease spreading over long distances, like onto other continents. As such, one of the key wheat blast mitigation strategies is in the hands of the world’s governments. The paper recommends quarantining potentially infected grain and seeds before they enter a new jurisdiction.
Governments can also create wheat “holidays”, which functionally ban cultivation of wheat in farms near regions where the disease has taken hold. Ideally, this would keep infectable crops out of the reach of wheat blast’s airborne and wind-flung spores. In 2017, India banned wheat cultivation within five kilometers of Bangladesh’s border, for instance. The paper also recommends that other crops — such as legumes and oilseed — that cannot be infected by the wheat blast pathogen be grown in these areas instead, to protect the farmers’ livelihoods.
Other tactics involve partnerships between researchers and agricultural workers. For instance, early warning systems for wheat blast prediction have been developed and are being implemented in Bangladesh and Brazil. Using weather data, these systems alert farmers when the conditions are ideal for a wheat blast outbreak.
Researchers are also hunting for wheat varieties that are resistant to the disease. Currently, no varieties are fully immune, but a few do show promise and can partially resist the ailment depending upon the disease pressure. Many of these resistant varieties have the CIMMYT genotype Milan in their pedigree.
“But the resistance is still limited. It is still quite narrow, basically one single gene,” Xinyao He, one of the co-authors of the paper said, adding that identifying new resistant genes and incorporating them into breeding programs could help reduce wheat blast’s impact.
Wheat spikes damaged by wheat blast. (Photo: Xinyao He/CIMMYT)
The more the merrier
Other methods outlined in the paper directly involve farmers. However, some of these might be more economically or practically feasible than others, particularly for small-scale farmers in developing countries. Wheat blast thrives in warm, humid climates, so farmers can adjust their planting date so the wheat flowers when the weather is drier and cooler. This method is relatively easy and low-cost.
The research also recommends that farmers rotate crops, alternating between wheat and other plants wheat blast cannot infect, so the disease will not carry over from one year to the next. Farmers should also destroy or remove crop residues, which may contain wheat blast spores. Adding various minerals to the soil, such as silicon, magnesium, and calcium, can also help the plants fend off the fungus. Another option is induced resistance, applying chemicals to the plants such as jasmonic acid and ethylene that trigger its natural resistance, much like a vaccine, Singh said.
Currently, fungicide use, including the treatment of seeds with the compounds, is common practice to protect crops from wheat blast. While this has proven to be somewhat effective, it adds additional costs which can be hard for small-scale farmers to swallow. Furthermore, the pathogen evolves to survive these fungicides. As the fungus changes, it can also gain the ability to overcome resistant crop varieties. The paper notes that rotating fungicides or developing new ones — as well as identifying and deploying more resistant genes within the wheat — can help address this issue.
However, combining some of these efforts in tandem could have a marked benefit in the fight against wheat blast. For instance, according to Singh, using resistant wheat varieties, fungicides, and quarantine measures together could be a time-, labor-, and cost-effective way for small-scale farmers in developing nations to safeguard their crops and livelihoods.
“Multiple approaches need to be taken to manage wheat blast,” he said.
